The term “microbiome” is used to describe a community of microscopic organisms living in and on a host organism. Currently, there is a lot of interest in learning more about how specific microbiomes may affect the physiological processes of the host organism.

For example, research conducted on the gut microbiome in mice has shown that genetically obese mice have a higher proportion of certain bacteria than genetically thin mice.

Furthermore, when the gut bacteria from obese mice were transferred to the gut of lean mice, the lean mice gained body fat, “suggesting a causative effect of the microbiota on its host’s physiology.” Similarly, gut bacteria transferred from obese humans to mice increased fat deposition in the mice, while gut bacteria from lean humans transferred to genetically similar mice resulted in a leaner phenotype.

It has been theorized that newborn ruminants begin to establish their individual microbiome soon after birth with the introduction of bacteria from the dam. Recent research published in Microbiome theorizes that French kissing may have a health benefit to couples due to trading bacteria species via the saliva.

Likewise, when the dam licks off the newborn calf, a side benefit may be that she is inoculating her newborn with beneficial organisms that will help the calf in establishing its own microbiome. Research has demonstrated that the development of the rumen wall and subsequent digestive function is positively influenced by a diverse microbial population in the gut.


Supplementing the dairy cow’s natural microbiome

Inspired by the results of the mouse studies, researchers in Israel found that the relative proportions of two specific bacteria in the rumens of lactating dairy cows were strongly correlated with daily milkfat yield.

These results suggest that there is tremendous potential for utilizing direct-fed microbials (probiotics) to supplement natural microbiomes and improve the physiological outcomes of the target host animal.

Because so much of the dairy cow’s digestion and subsequent metabolism is dependent on the work of microbes, it is no surprise that there is interest in further investigating the ways we can impact the dairy cow’s physiological processes by manipulating the bacterial population in the rumen and lower GI tract.

There are numerous feed additives that feature probiotic bacteria which deliver beneficial effects to dairy cows. Research trials have shown that specific probiotic feed additives have improved animal gut health by regulating pH, scavenging oxygen, binding pathogens and toxins, and inhibiting pathogenic bacteria.

These modes of action can result in an improvement in starch and fiber digestibility and decrease the incidence of sub-acute rumen acidosis (SARA), while field trials have demonstrated a 3- to 4-pound increase in energy-corrected milk.

Bacteriocins from E. faecium

Certain lactic acid bacteria produce antagonistic substances, called bacteriocins, which in very small amounts are extremely active against pathogens, especially those that compete for the same nutrient pool. Bacteriocins are non-toxic, proteinaceous compounds, more specific than antibiotics, and are a desirable part of the competitive exclusion process.

One particular strain of Enterococcus faecium is known to produce two specific bacteriocins that work together to inhibit the growth of pathogenic organisms such as Clostridium perfringens, Escherichia coli, Staphylococcus aureus and Streptococcus bovis.

By inhibiting the growth of these pathogenic organisms, this E. faecium strain helps boost the cow’s immune system, decreases fecal shedding and, consequently, the overall pathogen load in the environment is reduced. Additionally, research in 2012 demonstrated that ruminants fed an E. faecium probiotic had more immune cells in the small intestine than unsupplemented control animals.

Synergy of E. faecium and yeast

Even though they are fungi and not bacteria, live cell yeast are also considered to be direct-fed microbials. Research indicates that in addition to consuming oxygen and increasing rumen pH, certain live cell yeast can bind several pathogens. In an unpublished trial, the binding characteristics of a specific live yeast was found to significantly reduce the amount of E. coli and salmonella that was able to adhere to gut mucus.

The rumen is thought of as being an anaerobic environment, and the microbes responsible for digestion of feedstuffs in the rumen are anaerobes. However, through the ingestion of feed and the oxygen-carrying capacity of blood as it exchanges nutrients at the rumen wall, there is a fair amount of oxygen entering the rumen.

Since the native rumen microbes are obligate anaerobes, the reduction of oxygen in the rumen would have a positive effect on their growth and population. Live yeast and E. faecium are both capable of using aerobic as well as anaerobic fermentation pathways and are known to consume oxygen.

Because of this, their presence in the rumen helps increase the population of oxygen-sensitive microbes, such as Megasphaera elsdenii, responsible for converting lactic acid to propionate which increases rumen pH.

In a recent study, mid- and late-lactation cows were induced with sub-acute rumen acidosis, or SARA, and a control diet was compared to diets containing probiotics to see if the probiotics would be able to regulate pH.

The study found that the average daily pH tended to be higher, the minimum pH attained with SARA was higher, and the proportion of time pH was greater than 5.6 was greater when feeding a specific DFM with E. faecium than with the control or other probiotic treatments. Another trial in 2014 showed that feeding this same DFM during SARA reduced the drop in daily milk yield by 14.74 pounds compared to the control diet.

Competitive exclusion

Probiotics may also help the ruminant animal by a process known as competitive exclusion. Competitive exclusion (also known as Gause’s Law) states that two species that compete for the exact same resources cannot coexist in stable populations.

Pathogenic bacteria in the lower gut can cause damage when they adhere to and colonize epithelial surfaces such as the lining of the small intestine. If the pathogen is successful at infecting and damaging the epithelial cells, the pathogen may be able to cross the epithelial barrier where they can cause disease.

At the same time, beneficial, non-pathogenic bacteria demonstrate tactics associated with competitive exclusion when they compete with pathogens for nutrients and attachment sites on the epithelial cells.

While these beneficial, non-pathogenic bacteria are a normal part of the dairy cow’s microbiome, it makes sense that supplementing additional beneficial bacteria in the form of probiotics will increase the protection against pathogenic bacteria, reduce infections and strengthen the immune system.

While there is still a lot to learn about the microbiome of the dairy cow, numerous research projects have shown that supplementing specific probiotics to increase the microbial diversity of the cow’s gastrointestinal tract is beneficial.

Probiotics can help improve starch and fiber digestibility, improve the production of energy-corrected milk, decrease SARA and improve gut health of the cow. The addition of probiotic supplements being fed in dairy cow diets is sure to increase as producers realize the economic benefits from the adoption of this technology.

Additionally, we expect that there will continue to be new developments in this field that will lead to new opportunities for producers to benefit from increasing the diversity of the dairy cow’s natural microbiome. PD

Keith A. Bryan, Ph.D., is Americas Technical Services Manager, Silage Inoculants & Ruminant DFM, Chr. Hansen Animal Health & Nutrition.

References omitted due to spacebut are available upon request. Click here to email an editor.

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